A secondary battery is universally applied to an electric vehicle (EV) driven by an electric driving source, a hybrid vehicle (HV) or an energy storage system (ESS) or an uninterruptible power supply (UPS) system using a medium/large battery used for a house or an industry as well as a portable device.
When the secondary battery is implemented as a battery of a portable terminal, or the like, it may not particularly be applied as above, but in the case of the battery applied to the electric vehicle or an energy storage source, unit secondary battery cells are generally aggregated and used to increase suitability for a high-capacity environment.
The secondary battery stores and further, discharges energy while charging/discharging and further, overcharging of the secondary battery may generally cause a danger in safety due to a characteristic that the energy is accumulated. When an in-cell overcharge phenomenon of the secondary battery occurs, an air pore of a separator positioned between cathode and anode materials with an increase of temperature in the cell is closed, and as a result, a phenomenon in which the battery cell is swelled may occur and an explosion phenomenon may occur.
Therefore, a safety circuit against the overcharge is particularly provided in a battery device, and as a result, a device is required, which prevents further charging before the battery is ignited and exploded while charging and a device that interrupts current which flows on the cell of the secondary battery is referred to as a current interrupt device (CID).
Meanwhile, since overdischarge of the battery reduces life-span durability of the battery due to a characteristic in which the energy is consumed, the current interrupt device operates when not only the battery is overcharged but also the battery is overdischarged and when a battery user uses the battery while not recognizing that the current interrupt device is opened while discharging the battery, more excessive current than the battery cells included in another battery unit may flow in the battery cells included in the battery unit in which the current interrupt device is opened, and as a result, there is a risk of the ignition.
Therefore, an apparatus that can sense whether the current interrupt device is opened during discharging of the battery is required for the battery together with the current interrupt device, but in the related art, the apparatus that that senses whether the current interrupt device of the battery cell is opened does not exist during the discharging of the battery and the battery user may not know whether the current interrupt device is opened, and as a result, the battery user is exposed to the risk of the ignition.
In the present invention, when the battery is discharged, a situation in which the current interrupt device is opened is immediately announced to the user to allow the user to take an action against the corresponding situation in advance, thereby preventing a safety situation such as the ignition.